Don't you think it will give scammers the chance to misslead whoever is reading their trust feedbacks by spreading lies, if so, the one who left the feedback have to respond and so on.
If a user thinks the feedback he got was unfair, all he has to do is to complain about it on the reputation board and asks DT members to counter it. What I suggest is to make the countering feedback shows just bellow the countred one and not according to the chronological order.
True that. That also won't stop the retaliatory -ve feedback and the original rater will more likely do the same thing. So it's the same with extra comments.